The goal of this research is to identify an appropriate animal model for use in studying the effects of long-term noise on the inner ear of humans. Specifically, we are investigating the possibility of the squirrel monkey as the animal model by comparing the effects of a variety of noises on man and monkey. The approach is to replicate industrial working conditions by using recorded factory noises and work-day durations in addition to other exposure conditions. This will enable us to compare the effects of a variety of noises on man and monkeys as well as to compare the effects of commonly used laboratory noises with those of recorded factory noises. Three different institutions are combining their skills and facilities to perform simultaneous testing of humans and monkeys under extremely similar conditions, and to monitor concurrently the anatomical changes within the monkey inner ear. Once an appropriate animal model has been determined by these systematic investigations, the effects of noise exposure producing both TTS and PTS can properly be examined. Such studies should help to develop better damage risk criteria and compensation standards and reduce hearing loss due to long exposures to noises.